1. Field of the Invention
The present invention relates to a method and an apparatus for testing a lamp, and more specifically, to a method and an apparatus for measuring the performance of a lamp.
2. Description of the Prior Art
Digital projector (e.g. LCD digital projector or DLP digital projector), like a typical projector or a slide projector, uses a high brightness lamp to project images onto a screen. Digital projector includes optical devices to control the projection, and each of them would influence the quality of the projection. The lamp is the most influential because it is a light source for forming an image. A lamp with bad performance (e.g. brightness and uniformity) may cause bad quality of image projection.
As known by the industry, the lamp is composed of a burner and a reflector, and the relative position of the burner and the reflector affects the brightness and uniformity of the lamp. Generally, the lamp is tested by using an integrating sphere to calculate the light flux of the lamp. The larger the light flux is, the brighter the lamp is and the better the performance is. However, two lamps having the same light flux may lead to different image quality when respectively used in the same digital projector. Because when the lamp is installed in the digital projector, the light generated by the lamp outputs through an aperture, and only the light passing through the aperture contributes to the image formation. As it is mentioned above, the integrating sphere calculates the light flux of the lamp, but the projector utilizes only a portion of the light generated by the lamp. In other words, even if the two lamps have the same light flux calculated by the integrated sphere, each brightness and uniformity may be different, so that the digital projector using the lamps may project images in different quality.
For the manufacturer of lamp, lamp testing is mainly measuring lamp brightness by using the integrated sphere, which does not provide a reliable means to measure the real performance of the lamp. No other characteristics can be provided to adjust the relative position of the burner and the reflector of the lamp for a better and a uniform performance. In addition, the manufacturer of the digital projector can only require the manufacturer of the lamp for lamps with predetermined light flux. When testing the digital projector, a tester measures the brightness and uniformity of image projection only by the naked eye without an objective measurement to rank the brightness and uniformity of the lamp, so that reliable measured values cannot be obtained to select the lamps, and the qualities of the digital projectors will be all different due to the unstable qualities of the lamps.